Glycosyltransferase and sulfotransferase activities in chick corneal stromal cells before and after in vitro culture.

The expression type of proteoglycan in corneal stromal cells is known to change markedly when the cells are cultured in vitro. To determine which enzyme is primarily responsible for this change in chick corneal stromal cells, the activities of various glycosyltransferases and sulfotransferases were determined before and after in vitro culture of the cells. The activities of N-acetylglucosaminyltransferase, galactosyltransferase, and sulfotransferase, which are involved in keratan sulfate synthesis, were assayed using pyridylaminated N-acetyllactosamine-containing oligosaccharides as acceptor substrate; the activities of N-acetylgalactosaminyltransferase, glucuronyltransferase, and sulfotransferase, which are involved in chondroitin sulfate synthesis, were assayed using pyridylaminated chondrooligosaccharides as acceptor substrate. Of these enzymes, the sulfotransferase activity toward degalactosylated, pyridylaminated lacto-N-neotetraose and N-acetyllactosamine dimer (probably GlcNAc-6-sulfotransferase) decreased markedly after in vitro culture, whereas the galactosyltransferase activity increased. The chondroitin sulfate-sulfotransferase activities toward pyridylaminated chondrooligosaccharides hardly changed after in vitro culture. The marked decrease in the activity of the keratan sulfate-sulfotransferase corresponds to the marked decrease in keratan sulfate biosynthesis when the cells are cultured in vitro. These findings suggest that keratan sulfate-sulfotransferase (GlcNAc-6-sulfotransferase) is a key enzyme in keratan sulfate biosynthesis and that its decrease is primarily responsible for the marked decrease in keratan sulfate synthesis after in vitro culture.